Dry-charged lead acid storage battery having partially recharged electrodes and method

ABSTRACT

A dry-charged lead acid storage battery has partially recharged electrodes which serve as a source of sulfate ions. An additional source of sulfate ions is also inside the battery container. In contrast to the partially or fully discharged electrodes in previous dry batteries, the electrodes of this invention are characterized by having active material in which the percent of lead sulfate in the active material at a specified distance from the center of the electrode grid decreases as the specified distance of the material from the grid decreases. These improved electrodes are produced by being fully charged, then completely discharged, then partially recharged, and then washed and dried.

United States Patent Inventor Joseph C. Duddy Trevose, Pa.

App]. N 0. 874,276

Filed Nov. 5, 1969 Patented Sept. 21, 1971 Assignee ESB IncorporatedPhiladelphia, Pa.

DRY-CHARGED LEAD ACID STORAGE BATTERY HAVING PARTIALLY RECI-IARGEDELECTRODES AND METHOD 2 Claims, I Drawing Fig.

[1.8. CI 136/26, 136/27, l36/76, 136/34 Int. Cl ..H0lm39/00 Field ofSearch 136/26, 27, 76, 6, 33, 34, 161

LEGEND [56] References Cited UNITED STATES PATENTS 3,447,969 6/1969Tudor et al. 136/26 Primary Examiner-Winston A. Douglas AssistantExaminer-C. F. Lefevour Attorneys-Alfred J. Snyder, Jr., Robert H.Robinson and Raymond L. Balfour ABSTRACT: A dry-charged lead acidstorage battery has partially recharged electrodes which serve as asource of sulfate ions. An additional source of sulfate ions is alsoinside the battery container. In contrast to the partially or fullydischarged electrodes in previous dry batteries, the electrodes of thisinvention are characterized by having active material in which thepercent of lead sulfate in the active material at a specified distancefrom the center of the electrode grid decreases as the specifieddistance of the material from the grid decreases. These improvedelectrodes are produced by being fully charged, then completelydischarged, then partially recharged, and then washed and dried.

cuuzeev ACTIVE MATERIAL. (noes new CONTNN P650) H M! l COMPLETELYUNCHAMBD FU LLY CHARGED Tl ME 5 Tl PAITlALl-Y DI'SCHARGED 4. COMPLETELYDlbCHARCaED Tl ME .5 PAI'HALLV EEC-HAEQED TlME -I- DRY-CHARGED LEAD ACIDSTORAGE BATTERY HAVING PARTIALLY RECl-IARGED ELECTRODES AND METHODBACKGROUND OF THE INVENTION Among the disadvantages of todaysdry-charged lead acid automotive batteries is the fact they areactivated by the addition of sulfuric acid, a time-consuming, hazardous,and annoying process for the attendant doing the work. A second drawbackresults from the requirement to give the battery a charge after addingthe acid and before placing the battery in service, a time-consumingstep of inconvenience both to the attendant and to the car ownerawaiting the battery before he can drive away.

Attempts to eliminate the hazards associated with handling acid, as wellas hopefully to reduce the time required to activate and charge, havebeen made by storing inside the battery container a substance which inthe presence of water will produce the batterys electrolyte. In someinstances this substance is simply highly concentrated liquid sulfuricacid which upon addition of water will be diluted to the desiredconcentration, while in others it is some other sulfate ion compound(frequently a solid or semisolid gelatinous compound) which will reactwith or dissolve in water to produce sulfuric acid of the desiredstrength. Whatever the substance may be, one of the problems associatedwith its storage inside the battery container is the fact that theavailable space inside the container is severely limited, and simplyincreasing the dimensions of the container to increase the internalspace is not always a possible or desirable solution. One of the bigefforts of the internal storage approach, then, is to use everyavailable measure of space inside the container.

One location inside the container where sulfate ion compounds might bestored is in the electrodes themselves. When the battery is in thedischarged condition the active material of both the positive andnegative electrodes is a sulfate ion containing compound, PbSO whichwill react electrochemically with water to produce sulfuric acid, and sopartially discharged electrodes may serve as a partial source of sulfateion supply, supplementing the quantities stored elsewhere and in otherforms inside the container. An inherent drawback of this approach isthat while the desire is to have a battery which has already beencharged in the manufacturing plant and can therefore be quicklyactivated later at a service station without a booster charge, to usethe electrodes as a storehouse for sulfate ions requires the electrodesto be at least partially discharged. Nevertheless one form of thisapproach has been tried in a manner to be described in the paragraphsbelow.

The manufacturing process used to produce dry charged batteries involvesimmersing the positive and negative electrodes, both of which initiallycontain a lead compound active material consisting of mainly PbO (minorquantities of PbSO, are also present), into sulfuric acid, where thereis an immediate chemical reaction in electrodes of both polarity, PbO+HSO PbSO,+H O. The electrodes are then formed or charged," a step inwhich the PbSO, is electrochemically converted into a higher oxidationstate, PbO at the positive electrode and into a lower oxidation state,Pb, at the negative electrode. The electrodes are then washed, followingwhich the final step is to dry them. The drying must be done to removewater which otherwise would slowly, unintentionally, and undesirablyactivate the battery as it sits on the shelf awaiting usage. The dryingmust be done in a manner such that the act of drying will in itself notdischarge the electrodes, e.g., primarily a danger of oxidizing theelemental lead in the negative electrodes.

In the past if it was desired to use the electrodes as a storehouse forsulfate ions, they were simply partially of fully discharged after beingfully charged" or formed, thus electrochemically reconverting some orsubstantially all of the PbO, in the positives and the Pb in thenegatives back into Pb- SO Thus the sequence of electrode processing wasfully charging, partially or fully discharging, washing, and drying.

Since the electrochemical reactions begin at the surface of the gridwhere there is an interface between the electrically conductive grid,the active material, and the sulfuric acid, and slowly progressoutwardly toward the exterior of the electrode, this meant that at theconclusion of the partial discharge step there was a PbSO, gradient inthe active material, a gradient in which the percent of lead sulfate inthe active material at a specified distance from the center of theelectrode grid increased as the specified distance of the material fromthe grid decreased. In short, the closer to the grid one looks, thegreater the percentage of PbSO, in the active material he would find.

With the previous method described! above, at the end of a partialdischarge step the exterior of each electrode was relatively rich incharged active material (PbO in the positive, Pb in the negative) whilethe interior was relatively rich in the discharged form of the lead,PbSO PbSO is well recognized to be a poor conductor of electricity. Theresultant electrodes of this previous method therefore had the followingcharacteristics: (a) the charged active material, which should beclosest to the grid to give greatest cranking power from the battery,was predominantly in the most remote possible location with respect tothe grid; and, (b) by having a high proportion of PbSO, near the centerof the electrode, there was in ef feet a layer of poorly conductivematerial between the charged active material and the grid. Thus thereexisted a gradient, a ratio of charged to discharged material at aspecified distance from the grid center which varied as the distancefrom the grid center also varied, and this gradient was in theunfavorable direction.

SUMMARY OF THE INVENTION The invention consists of a recognition thatthe PbSO, gradient of previous dried, partially discharged electrodeswas unfavorable and the discovery of a simple way to make the gradientmore favorable.

The present invention consists of making the PbSO, gradient morefavorable. The process of manufacturing drycharged electrodes accordingto the present invention, beginning with the conventional greenelectrodes having PbO active material in both the positive and negativeelectrodes, consists of fully charging, then completely discharging,then partially recharging, and then washing and drying the electrodes.The results are electrodes characterized by having active material inwhich the percent of lead sulfate in the active material at a specifieddistance from the center of the electrode grid decreases as thespecified distance of the material from the grid decreases. The benefitis that, compared with electrodes of the prior partial discharge processhaving the same total ratio of charged to discharged active material inthe total of all active material in the electrodes, the electrodesproduced by this invention yield a battery having better crankingcharacteristic immediately after activation.

BRIEF DESCRIPTION OF THE DRAWING The drawing illustrates a lead acidbattery electrode, either positive or negative, in various states ofcharge and discharge. The illustrations of the electrode are taken atfive different times, and are shown in the time sequence in which theywould occur using the present invention.

The five illustrations represent oversimplifications of the degree towhich active material at a specified distance from the center of theelectrode grid is charged or discharged. In actual fact the activematerial at a given distance from the center of the grid will likelycontain both charged and discharged material, even in electrodescommonly described as being fully charged" or completely discharged."(Neither charging nor discharging is totally effective in actualpractice, and in common usage such terms as fully charged" andcompletely discharged" refer to the conditions which exist after suchactual charging and discharging are complete and discontinued.) Also inactual fact there is no sharp boundary between the charged anddischarged material, but rather a gradual gradient such as is discussedin the Background and Summary sections above would exist. Despite theerrors resulting from oversimplification, the five illustrations in thedrawing will serve to illustrate conceptually the method and result ofthe present invention.

The center lines in the five illustrations are intended to represent thecenter of the electrode grid. If the electrode is a flat plate such asis conventional in automotive batteries in the United States today, thegrid is also a skeleton, platelike structure and the center of the gridis a plane. If the electrode is a circular object such as the tubularelectrodes commonly used today in lead acid batteries for motive-powerpurposes, the center of the grid is the grids lineal axis. The activematerial surrounds the grid.

Time 01 is at the beginning of the time sequence with which the presentinvention is concerned, namely when the electrodes are completelyuncharged and the formation" has not yet begun, or at its verybeginning. At that time the lead active material in both the positiveand negative electrodes is mostly PbO.

Time 02 is later in the formation process, when the electrodes are fullyformed or charged. At this time the active material in the positiveelectrodes is substantially all PbO while the active material in thenegatives is substantially all Pb.

Time 03 is still later, after the electrodes shown at Time 02 have beenpartially discharged. At Time 03 the interiors of both the positive andnegative electrodes will contain a greater percentage of F'bSO than willtheir exteriors. Time 03 represents the point at which the partialdischarge step of the previous method described in the Backgroundsection above has been stopped and the washing and drying begun.

Time 04 is still later, when the discharging shown in a partiallycomplete stage in Time 03 has been carried to completion. The activematerial in both positive and negative electrodes at Time 04 issubstantially all PbSO Time 05 is still later, after the completelydischarged electrodes shown at Time 04 have been partially recharged. AtTime 05 the interiors of both the positive and negative electrodes willcontain a smaller percentage of PbSO, than will their exteriors.

The symbol used in the drawing to designate noncharged active materialis used for both uncharged material (that which has never been charged)and for discharged material (that which has previously been charged,then discharged). The use of a common symbol in the drawings is notintended to imply that uncharged and discharged materials are identical(in fact they are not), but only to imply a distinction between chargedand noncharged material.

DESCRIPTION OF THE PREFERRED EMBODIMENT From what has already beenstated in the Background, Summary, and Description of the Drawingsections, an understanding of the invention should by now be clear.

The invention consists both of a method for producing drychargedelectrodes and a battery containing such electrodes. The first step inthe method consists of immersing an electrode having a lead compoundactive material into a sulfuric acid solution. This step is symbolizedby Time 01 in the drawing, when the active material is mostly PbO inboth positives and negatives, referred to as completely uncharged in thedrawmg.

The next step consists of charging the electrodes to a state ofsubstantially full charge, shown as Time 02. The term substantially fullcharge is used rather than full charge, both because (as stated above)the active material in fact is usually not 100 percent charged even whenin the state commonly described as fully charged," and also because itis desirable but not essential to charge the electrodes up to thecondition commonly described as fully charged,"

The next step in the method of this invention consists of dischargingthe electrodes to a state of substantially complete discharge, shown asTime 04 in the drawing. The qualifying termsubstantially is used forreasons similar to those stated in the preceding paragraph. Whilecarrying out this step of the process the electrodes pass through astate represented by Time 03 in the drawing.

Next, the electrodes are recharged to a state of partial charge. Therate of recharging is variable, but should be at such a rate that theactive material on the interior of the electrode, but not much of theactive material on the exterior, is charged. The exact time, the exactratio of charged to discharged active material at a specified distancefrom the center of the grid in either positive or negative electrodeswhen this step is discontinued is not critical and is essentially amatter which results from the designers choice of recharging rates andother factors. At Time 05 the interiors of both the positive andnegative electrodes will contain a higher percentage of charged activematerial, PbO and Pb respectively, than will their exteriors, thecondition which this invention seeks to achieve; but the electrodes ofboth polarity will also contain some discharged active material, PbSOwhich is desirable from the point of view that it represents storedsulfate ions which can serve as a partial source of supply to producesulfuric acid after water is added, but which is undesirable from thepoint of view that it represents discharged active material which willlater have to be charged (although not necessarily charged before thebattery is placed in service in an automobile).

The final steps of the process are washing and drying of the electrodes,which may be carried out with conventional techniques.

The products which result from this process are ones in which thepercent of lead sulfate in the active material at a specified distancefrom the center of the electrode grid decreases as the specifieddistance of the material from the grid decreases.

The electrodes may be used in an otherwise conventional battery, onehaving a conventional container, cover and terminals. The terminalsconstitute means for conducting electrical current between the exteriorof the container and the positive electrodes inside the container, aswell as additional means for conducting electrical current between theexterior of the container and the negative electrodes inside thecontamer.

An additional component of the dry-charged battery of this invention isa source of sulfate ions inside the container which is in addition tothe PbSO, active material in the electrodes. The present invention isnot to be limited as to the specific composition of that additionalsource, whether merely concentrated liquid I-I SO, or some othersubstance which will react with or dissolve in water to produce liquid HNeither is it limited to the location of that additional source, whetherin the otherwise unoccupied space inside the container above, beside, orbeneath the electrodes, or whether included in or comprising theseparators between the electrodes. And neither is the invention confinedto batteries in which the additional source of sulfate ions is confinedor restrained in some manner, either to prevent the substance fromabsorbing any moisture which might remain in the dried electrodes or toprevent the acid from damaging the separators during storage orimmediately after water addition; this category of batteries includesones in which the sulfate ion substance is confined in plasticcontainers opened by a variety of methods.

Test results indicate that a cell made according to the presentinvention yields better cranking characteristics at a given time afteractivation than a cell otherwise identical but having electrodesrepresented by the illustration in the drawing designated as Time 03.For comparison purposes four Group 24 size cells of 60 ampere hourcapacity (at the 20 hour discharge rate) and having electrodes andseparators of conventional and identical design were discharged.Discharge during testing was at a constant current rate of 150 amps andwas at a temperature of 110 F.; discharge of the cells was begun 15minutes after addition of water and the extra sulfate ions to thedry-charged cells, and without any booster charge having been given. Thefirst cell, used as an absolute reference, was a wet, fully charged cellrather than one which has been dry-charged; the specific gravity of itsH SO ,elec trolyte was 1,270. The second cell was a dry-charged onehaving half-discharged electrodes represented by illustrations as Time03 in the drawing. The third cell was also a dry-charged one havinghalf-recharged electrodes represented by illustrations as Time 05 in thedrawing. (Byhalf-discharged, halfcharged, and half-recharged" is meantthat 50 percent is discharged.) In both the second and third cells therate of charging and discharging was held constant at a 5 ampere rate.The additional source of sulfate ions supplied to each of the second andthird cells was 180 cc. of H SO having a specific gravity of 1.700; toeach of these two cells 530 cc. of water was also added, and theresultant electrolyte has a specific gravity of approximately 1.210. Thefourth cell also had dried electrodes, but they were conventionallydry-charged and were substantially completely charged; the specificgravity of the electrolyte in the fourth cell was 1.27.

The cell voltages are shown in Table 1:

Table 1 Time Cell 01 Cell 02 Cell 03 Cell 04 (measure (wet, fully (dry,half- (dry, half (dry, fully ments for charged), discharged rechargedcharged Cells 2-4 Volts electrodes), electrodes), electrodes), beginning15 Volts Volts Volts minutes after activation 5 secs. 1.81 1.64 1.691.74

30 secs. 1.82 1.63 1.68 1.73 l min. 1.80 1.60 1.67 1.72

15; min. 1.57 1.65 1.70 2 min. 1.79 1.54 1.64 1.69 2% min. 1.52 1.621.68 3 min. 1.78 1.47 1.61 1.66 3 min. 1.40 1.60 1.64 4 min. 1.76 1.581.63 4% min. 1.55 1.61 5 min. 1.74 1.52 1.59 5% min. 1.49 1.56 6 min.1.72 1.50 6 min. 1.40 7 min. 1.70

8 min. 1.66

9 min. 1.62

10 min. 1.53

The most interesting comparison, the one which compares the cell of thepresent invention with its counterpart made under the previous method,is between the results of Cell 02 and Cell 03. Cell 03, the one of thepresent invention, comes much closer than does Cell 02 to the desiredgoal of letting a car owner install a freshly activated battery in hiscar and drive away without waiting a long time for the battery toreceive a booster charge. After engine-starting the generator oralternator could be used to charge the discharged material in theelectrodes, and this could be done while the car was being driven.

The step of completely discharging the electrodes so that they may bepartially recharged again is more time consuming than the previousmethod but is not necessarily very wasteful of electrical energy, sincea circuit for discharging one group of electrodes can well be the sourceof power for charging another group of electrodes.

During the initial charging or forming step the electrodes will undergoa transition during which the active material in their interiors will bemore fully charged than it will be in their exteriors, and consequentlythe electrodes will have active material in which the percent of leadsulfate in the active material at a specified distance from the centerof the electrode grid decreases as the specified distance ofthe'material from the grid decreases. During the initial charging,therefore, the electrodes are between the stages represented by Times 01and 02in the drawing and are at a stage which, if it were to be shown onthe drawing, would appear identical to the condition represented by Time05. In fact these electrodes which have never been fully charged onceand are only partially charged are quite different from ones which havebeen fully charged, then fully discharged, and subsequently partiallyrecharged, even though the percents of charged and recharged activematerials might be the same at the two times. It is well recognized inthe battery art that until the electrodes have been fully charged atleast once their active material has very poor charge acceptance.

1 claim:

1. A method of producing a partially charged and dry electrode for alead acid battery comprising the steps of:

a. immersing an electrode having a grid surrounded by lead compoundactive material comprising PbO into a sulfuric acid solution;

b. charging the electrode to a state of substantially full charge;

0. discharging the electrode to a state of substantially completedischarge;

d. recharging the electrode to a state of partial charge whereby theelectrode is characterized by having active material in which thepercent of charged active material increases over a specified distancefrom the center to the exterior of the electrode as the distance fromthe grid decreases and in which the percent of lead sulfate decreasesover a specified distance from the center of the electrode grid to theexterior of the electrode as the distance from the grid decreases;

e. washing the electrode; and,

f. drying the electrode.

2. A dry-charged lead acid storage battery having a. a container,

b. dry positive and negative electrodes within the container which havepreviously been fully charged, each electrode consisting of a gridsurrounded by lead compound active material, the lead compound activematerial in the positive electrode comprising an oxide of lead-chargedmaterial and lead sulfate discharged material and the lead compoundactive material in the negative electrode comprising lead chargedmatcrial and lead sulfate discharged material,

. a source of sulfate ions inside the container which is in addition tothe electrodes,

(1. a cover on the container, and

e. means for conducting electrical current between the exterior of thecontainer and the positive electrodes and additional means forconducting electrical current between the exterior of the container andthe negative electrodes, wherein the improvement comprises:

each of the positive and negative electrodes characterized by havingactive material in which the percent of charged active materialincreases over a specified distance from the center of the electrodegrid to the exterior of the electrode as the distance from the griddecreases and in which the percent of lead sulfate decreases over aspecified distance from the center of the electrode grid to the exteriorof the electrode as the distance from the grid decreases.

1. A method of producing a partially charged and dry electrode for alead acid battery comprising the steps of: a. immersing an electrodehaving a grid surrounded by lead compound active material comprising PbOinto a sulfuric acid solution; b. charging the electrode to a state ofsubstantially full charge; c. discharging the electrode to a state ofsubstantially complete discharge; d. recharging the electrode to a stateof partial charge whereby the electrode is characterized by havingactive material in which the percent of charged active materialincreases over a specified distance from the center to the exterior ofthe electrode as the distance from the grid decreases and in which thepercent of lead sulfate decreases over a specified distance from thecenter of the electrode grid to the exterior of the electrode as thedistance from the grid decreases; e. washing the electrode; and, f.drying the electrode.
 2. A dry-charged lead acid storage battery havinga. a container, b. dry positive and negative electrodes within thecontainer which have previously been fully charged, each electrodeconsisting of a grid surrounded by lead compound active material, thelead compound active material in the positive electrode comprising anoxide of lead-charged material and lead sulfate discharged material andthe lead compound active material in the negative electrode comprisinglead charged material and lead sulfate discharged material, c. a sourceof sulfate ions inside the container which is in addition to theelectrodes, d. a cover on the container, and e. means for conductingelectrical current between the exterior of the container and thepositive electrodes and additional means for conducting electricalcurrent between the exterior of the container and the negativeelectrodes, wherein the improvement comprises: each of the positive andnegative electrodes characterized by having active material in which thepercent of charged active material increases over a specified distancefrom the center of the electrode grid to the exterior of the electrodeas the distance from the grid decreases and in which the percent of leadsulfate decreases over a specified distance from the center of theelectrode grid to the exterior of the electrode as the distance from thegrid decreases.